In their earliest forms, display systems such as televisions or computer monitors displayed a single program or series of images from a single source, such as a selected television station or program. Within the field of television, a "picture-in-picture" system was developed. This system allowed the television to display a television program on the entire screen, in conventional format, and in addition to display a smaller picture from a different channel, in shrunken form, on the same screen. In essence, such systems comprised two television pictures on one screen, a main picture comprising a standard television picture and a smaller subpicture called the PIP ("picture-in-picture"). Typically, the PIP was less than 1/4 of the size of the screen. The PIP ordinarily resided in the lower right quadrant of the main picture, though with a border of the main picture surrounding the PIP. Typically, the PIP provided an apparently complete image of the second channel to the viewer. While in actuality, various bits of information, denominated pixels, were dropped from the actual displayed PIP, given the relatively smaller size of the PIP, the image appeared substantially complete to the viewer.
Analog television technology generally did not permit the displaying of multiple images from multiple channels, such as in a PIP system. In the case of analog television technology, the main picture set to a first channel was derived from a first television station and the second channel for the PIP was derived from a second television station. Since the analog television system displayed images via a raster scanned CRT where the image information was received via the broadcast and synchronized with the monitor by a timing pulse (sync pulse) there was no necessary correlation for synchronization between the two channels. By way of example, one channel could be scanning the upper left portion of the picture while the second channel would be scanning the bottom left portion of the picture. Synchronization in analog systems was generally not feasible.
Digital electronics facilitated generation of overlapping displays. In certain versions, the main picture was generated and displayed as before. The PIP was generated by a PIP circuit which stored images, or selected pixels of the image, coming from the second channel. Information regarding the scanning location on the main picture was provided to the PIP circuitry. Through this synchronization, the PIP circuitry provided output to the screen or monitor at the appropriate time. The image information in the PIP circuitry was stored in digital memory. That image information was updated as received from the channel. In this way, the raster scanned display provided the main picture as received from the television station and the PIP circuitry provided a imperceptively delayed PIP. In this way, the synchronization problem was overcome.
The result of the PIP system was that there were, in essence, two television channels or pictures being displayed on one screen. Each tuner could be set independently. In this way, the viewer could select a first channel for display on the main picture and a second channel for display on the PIP. In use, the PIP feature was particularly advantageous for watching two shows in which the time during which action occurred was relatively minor compared to the overall program duration, such as in sporting events, especially in football. The viewer could tune each tuner to a separate game, with the PIP being large enough to provide a viewable image, especially one sufficient to inform the viewer of impending action. At that point, the viewer could change channels, causing the PIP to be displayed as the main picture.
A swap or exchange feature was often employed in PIP systems. This feature exchanged the main picture and PIP by activation of a single button. In the sports viewing example, above, the viewer could swap the channels, maintaining as the main picture the channel with the then current action. The swap feature typically was achieved by electronically switching the output from the two tuners, such that the output from the first tuner set to a first channel was supplied as input to the PIP circuitry, and the output of the second tuner set to the second channel was provided as the input to the main picture display circuitry. In this way, the tuners remained set at a given channel, and the outputs of the tuners were electronically switched as inputs for further processing.
While such PIP systems had good utility in the applications described, they were subject to operational limitations. Since the systems in essence provided two separate televisions combined for a display on one screen, the user was required to tune the two televisions, even prior to invoking a swap feature. Further, there is a latency period between displaying channels during a channel change operation. This latency between the time the channel change is initiated and the time at which the television displays the next channel may result in loss of desired information.
Computer display systems have utilized windows based display systems. A given window typically displays information from a source, such as a screen generated by a software program. These windows are often arranged in an overlapping arrangement. Certain systems permit toggling or cycling through various windows, such as to permit the user an unobstructed view of a complete window. Generally, such systems only change the contents of the currently selected window.
Accordingly, the current state of method and apparatus for the control of images from multiple sources has limits on the modes of operation.